There is a general consensus that energy needs to be obtained from renewable sources, from environmental, economical, and security perspectives. The resulting question of how to obtain such energy for transportation remains.
When one considers obtaining energy from biomass, two possibilities are to convert biomass into ethanol (for internal combustion engines), and to convert biomass into electricity (for battery-powered electric vehicles). Although both possibilities have potential, it is unknown which one is the better choice, from the perspective of land-use.
If, for example, one energy source is less efficient, and therefore requires more cropland to be set aside for energy utilization rather than food, it may be advisable to pursue the other energy source instead. However, thorough land-use considerations are often neglected when scientists debate the merits of biomass utilization for transportation.
Elliott Campbell (University of California, Merced) and coworkers have probed this issue. They have found that energy derived from biomass is more efficiently utilized as electricity for use by battery-powered electric vehicles than as ethanol for use in internal combustion engines, when only land-use considerations are taken into account.
A life-cycle assessment.
The scientists approached this issue from a life-cycle assessment of the plants processed into energy, and that of vehicle development and use. They utilized a computer model, called the Energy and Resources Group Biofuel Analysis Meta-Model.
This model takes many considerations into account, in order to fairly obtain a representative evaluation of the possibilities available for energy input and processing. These considerations include a range of plants for biomass utilization, the energy required to produce the plants and convert them into fuel, and the energy required to produce and dispose of the vehicles.
Bioelectricity may be superior.
The scientists found that the net transportation output, per unit cropland, is 112% greater for bioelectricity relative to bioethanol, averaged across all plants, energy conversions, and vehicle efficiencies. Analagously, they also found that the greenhouse gas offsets, per unit cropland, are 108% greater for bioelectricity relative to bioethanol.
In other words, for vehicles of the same size, one can travel further in a vehicle with a bio-powered electric battery than a bio-powered internal combustion engine, and the end result will be less polluting. Interestingly, the scientists propose that by utilizing carbon-capture technology and harvesting the steam produced by biomatter processing, carbon dioxide may actually be removed from the atmosphere, rather than added to it.
Words of caution.
Based on these considerations alone, one may conclude that bio-powered vehicles based on electricity are more favorable than ethanol. However, other factors, such as water utilization and pollution, were not considered here, and may not be in bioelectricity's favor.
Furthermore, the climate and health costs of ethanol derived from biomass can be higher than those of gasoline, depending on the method of combustion and the source of the plants. Utilizing biomass for energy is not inherently better for the environment than conventional petroleum.
Also note that there are other potential sources of energy for transport that were completely ignored in this evaluation, such as solar power. While this evaluation was carefully thought out and quite detailed, a broader evaluation of more energy sources, and criteria beyond what these scientists have analyzed, is still needed to conclusively resolve the issue of transportation needs in a more sustainable future.
for more information:
Campbell, J. E., Lobell, D. B., & Field, C. B. (2009). Greater Transportation Energy and GHG Offsets from Bioelectricity Than Ethanol Science, 324 (5930), 1055-1057 DOI: 10.1126/science.1168885